Maintenance & Reliability · SOP

Finishing Room Positive Pressure Verification

This PM log defines the calibrated instrument procedure to measure, record, and validate the positive static pressure differential of a finishing room (paint booth / powder coat / coating cell). Maintaining positive pressure prevents dust, airborne particulate, and uncontrolled humidity ingress that compromises coating adhesion and finish quality.

Estimated Time

30 min

Difficulty

Intermediate

Regulation

CSA Z432 / NFPA 33

Version

1.0

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Purpose

To provide a repeatable, documented method for verifying that the finishing room maintains a positive static pressure differential relative to adjacent spaces, in compliance with the facility's HVAC balancing schedule and NFPA 33 / CSA Z432 guidelines. Routine verification ensures airborne contaminants (dust, overspray mist, airborne fibres) cannot enter the finishing envelope, preserving coating quality and reducing rework.

Scope

This procedure applies to all conditioned finishing rooms within the facility — including liquid paint booths, powder coating cells, and UV-cure coating stations — that are designed to operate under positive pressure (typically 12.5–30 Pa relative to corridor / antechamber). It covers the weekly PM verification using a digital manometer, acceptable range criteria, corrective action triggers, and data logging requirements. Excluded: abrasive blasting rooms (negative pressure) and open-atmosphere spray areas.

Safety Precautions

LOTOLock out and tag out the finishing room HVAC supply fan disconnect before opening any access panels or static pressure port covers. Verify zero energy state with a non-contact voltage tester. Applies only if the instrument port requires removal of a guard or filter access door.
PPEWear safety glasses with side shields and steel-toed boots at all times in the finishing zone. If the fan room or air handler enclosure exceeds 85 dBA during measurement, wear hearing protection (ear muffs or plugs with NRR ≥25 dB).
CONFConfined space entry procedures apply if the static pressure port is located inside a ceiling plenum or fan plenum with restricted access. Do not enter without atmospheric testing (O₂, LEL, CO) and a standby attendant.
CHEMVerify that no solvent or coating spraying is active in the room during measurement. Volatile organic compounds (VOCs) may accumulate at the ceiling level; use a calibrated photoionization detector (PID) if there is any odour or process crossover.

Required Tools & Materials

Digital manometer, range 0–125 Pa, resolution ≤0.1 Pa, with valid calibration certificate (traceable to NIST or NRC, dated within 12 months)
Silicone tubing, 5 mm ID × 8 mm OD, 2.0 m length, with barbed fittings
Calibration log book or digital PM form (CMMS — ServiceGrid)
Ladder or step stool, rated height sufficient to reach static pressure port (typically 2.4 m above floor)
Temporary sealing tape (duct tape grade) for leak isolation if preliminary reading is out of range
Hygrometer / thermometer combination tool (±1°C, ±3% RH accuracy)
Pen and permanent marker for on-site annotations
Lockout/tagout kit (padlock, hasp, danger tag) — required only if access panel must be opened
Photoionization detector (PID) with 10.6 eV lamp — optional, for VOC presence check

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Procedure: Step-by-Step

1 Notify and isolate. Inform the production supervisor that the finishing room will be unavailable for 30 minutes during verification. Post "PM IN PROGRESS – DO NOT OPERATE" signage on all access doors. Confirm no coating activity is occurring inside the room.

2 Set up the manometer. Place the ladder to access the static pressure port located 300 mm above the door header on the interior (finishing) side of the main personnel door. Verify the manometer is zeroed (display reads 0.0 Pa with ports open to atmosphere). Connect the silicone tubing to the HIGH (+) port.

3 Measure interior static pressure. Remove the static pressure port cap. Insert the manometer tubing flush with the interior wall surface — do not allow the tube to protrude into the airstream. Wait 30 seconds for the reading to stabilize. Record the value as P_interior (Pa) on the PM log.

4 Measure exterior reference pressure. Move to the corridor side of the same wall. Connect the manometer tubing to the LOW (−) port. Open the exterior static pressure port cap. Insert the tubing flush with the wall surface. Wait 30 seconds. Record as P_exterior (Pa).

5 Calculate differential pressure. ΔP = P_interior − P_exterior. Acceptable range: 12.5 Pa ≤ ΔP ≤ 30 Pa for an ISO 8 (Class 100,000) finishing environment. Record ΔP on the log. If ΔP is below 12.5 Pa, proceed to Step 6a. If ΔP is above 30 Pa, proceed to Step 6b. If within range, skip to Step 7.

6a Correct low ΔP (<12.5 Pa). Check the makeup air unit (MAU) filter bank ΔP — if filter ΔP exceeds 125 Pa, replace filters. Verify the supply fan drive belt tension (deflection ≤20 mm at mid-span). Inspect motorized dampers for full-open position. Re-measure after each correction. Document all actions taken.

6b Correct high ΔP (>30 Pa). Inspect return air grilles and exhaust dampers for blockage, fully closed position, or inadvertent damper override from the BMS. Check for construction debris or tape covering openings. If an exhaust fan is running, verify sheave alignment and belt condition. Re-measure after each correction. Document all actions.

7 Record ambient conditions. At the same static pressure port location, measure and record room temperature (±1°C) and relative humidity (±3% RH). Acceptable ranges: 18–24°C, 40–60% RH. Close and tighten both static pressure port caps finger-tight — do not overtighten.

8 Finalize and close out. Remove ladder, tools, and signage. Inform the supervisor that the finishing room has been returned to service. Scan the completed PM log or enter the readings directly into the CMMS (ServiceGrid) under asset ID FIN-ROOM-PRESS-01. Attach any corrective action notes and schedule a 24-hour re-check if adjustments were made.

Finishing Room Positive Pressure Verification

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